Ions may be directed along a path by exposing the ions to electric and/or magnetic fields. The utilization of such fields to guide ions has numerous practical applications. A common use of multipole ion flow guides within analytical chemistry is as mass analyzers within mass spectrometers. A mass spectrometer is a device that identifies ions according to their mass-to-charge ratio. As the particle stream containing the ions to be analyzed passes through the mass analyzer, the ions are transmitted based on their mass-to-charge ratio towards a detector, which detects the ions based on their charge or momentum.
Ideally, only the ions to be analyzed reach the detector. It is often the case, however, that particles not of interest such as neutrals and photons reach the detector resulting in false signals. Additionally, the presence of neutral species in addition to the ions to be analyzed within a particle stream introduced into a mass analyzer may lead to fouling of the mass analyzer and/or other complications affecting the accuracy of the mass spectrometer.
For example, the particle stream introduced to the mass analyzer often undesirably contains photons. The presence of photons within the particle stream may lead to elevated background levels and/or increase the noise within the detector. In addition, the openings of some ion guides may be narrow and prone to contamination by the entering neutral species thereby causing instrument drift.